Searching for Axion Dark Matter from Cosmology to Condensed Matter

轴子是一类理论粒子，可以解释暗物质（DM）的奥秘。轴子的质量很小，在质子质量的万亿分之一到万亿分之一之间。寻找轴子就像是在调收音机，你不知道你想要的电台的频率，甚至不知道它是长波还是调频。为了找到轴子，我们需要许多不同类型的“无线电”（共振）来覆盖广泛的质量范围。我的研究着眼于最轻和最重的质量，利用宇宙学和实验室中的共振。这些检索的结果可以确定DM的性质。统计方法允许将结果解释为对两个特定理论的约束：“量子色动力学”（QCD）轴子和弦理论景观。宇宙学和天体物理学数据中的中微子。非常轻的轴子会影响宇宙的膨胀率和结构的增长。来自普朗克卫星宇宙微波背景（CMB）的数据限制了这些轴子最多只有DM的百分之几。然而，弦理论预测的丰度甚至更小，因此我们必须进一步推动数据分析和精确建模。使用在CMB中搜索轴子的相同技术，我将在其他数据中搜索轴子的证据。我将使用星系的引力透镜，即将到来的高精度CMB数据，以及氢气分布的射电天文学地图。利用其他天体物理学观测数据，我们可以将搜索范围扩大到稍重的轴子。我将寻找轴子波干扰星系中恒星运动的证据（流行的“模糊”DM模型）。最后，轴子可以影响黑洞旋转的速度。引力波探测可以精确测量黑洞的质量和自旋，因此可以用来寻找轴子的证据。在实验室中直接探测最重的DM轴子。在20世纪70年代，为了解决强核力（称为QCD）的对称性问题，人们预测了更重的轴子。从美国到韩国，有许多实验在寻找这种QCD轴子，因为它与电场和磁场相互作用。我已经提出了一种方法，在目前实验无法达到的频率范围内搜索QCD轴子，我想把全球轴子实验的复兴带到英国。“拓扑共振轴子探测”（TOORAD）的工作原理是，当一种叫做拓扑绝缘体的材料暴露在磁场中时，轴子激发出一个电场。制造材料本身具有磁性，电场激发磁共振，类似于医院中的核磁共振。然后，磁共振使材料发射光子。如果发射的光子可以被探测到，那么这种材料就可以用作轴子探测器。我建议发展一个国际合作来研究这个问题，并最终在一个合作实验室进行实验。QCD轴子模型的天体物理测试。当量子色动力学轴子在大爆炸期间产生时，产生的动力学使它形成大约有一颗大行星质量的致密团块：“微团”。搜索这些DM块是可能的，但也很难准确预测它们的质量和数量。我将建立必要的理论模型来回答这个问题。有了这些信息，我将通过两种方式搜索miniclusters的证据。首先，它们可以用引力透镜来发现，就像发现遥远恒星周围的行星一样;其次，当小星团与中子星等的磁场碰撞时，它们表现为辐射爆发。了解微星系团的质量和丰度对于精确预测地球实验室中的轴子信号也非常重要。

Axions are a class of theoretical particles that could explain the mystery of Dark Matter (DM). The axion mass is tiny, between one trillionth the mass of the proton and one billion-trillion-trillionth. Searching for axions is like tuning a radio where you don't know the frequency of the station you want or even if it is long wave or FM. To find the axion we need lots of different types of "radios" (resonances) to cover the wide range of masses. My research looks at the lightest and heaviest masses, using resonances in cosmology and in the lab. The results of these searches could identify the nature of DM. The statistical methods allow the results to be interpreted as constraints on two specific theories: the "quantum chromodynamics" (QCD) axion, and the string theory landscape. The Lightest Axions in Cosmological and Astrophysical Data. Very light axions affect the expansion rate and growth of structure in the Universe. Data from the Planck satellite cosmic microwave background (CMB) limits these axions to be at most a few percent of the DM. String theory, however, predicts that the abundance is even smaller, so we must push further in data analysis and precision modelling. Using the same techniques developed to search for axions in the CMB, I will search for evidence of axions in other data. I will use gravitational lensing of galaxies, upcoming high precision CMB data, and radio astronomy maps of hydrogen gas distribution. Using other astrophysical observables we can extend the search to slightly heavier axions. I will search for evidence of the axion waves disturbing the motion of stars in galaxies (the popular "fuzzy" DM model). Finally, axions can affect how rapidly black holes spin. Gravitational wave detections give precise measurements of black hole masses and spins and can thus be used to search for evidence of axions. Direct detection of the heaviest DM axions in the lab. Heavier axions were predicted in the 1970's to solve a problem about the symmetry of the strong nuclear force (known as QCD). There are many experiments, from the USA to South Korea, searching for this QCD axion, because it interacts with electric and magnetic fields. I have proposed a method to search for the QCD axion in a range of frequencies no current experiment can reach, and I want to bring the global renaissance in axion experiments to the UK."Topological Resonant Axion Detection" (TOORAD) works by the axion exciting an electric field inside a material called a topological insulator when it is exposed to a magnetic field. Manufacturing the material to be magnetic itself, the electric field excites a magnetic resonance, similar to NMR in hospitals. The magnetic resonance then causes the material to emit photons. If the emitted photons can be detected then the material can be used as an axion detector. I propose to grow an international collaboration to study this and eventually perform the experiment in a partner laboratory.Astrophysical test of the QCD axion model. When the QCD axion is produced during the big bang the dynamics of the production cause it to form dense clumps with about the mass of a large asteroid: "miniclusters". It is possible to search for these lumps of DM, but it is also very hard to predict exactly how massive they are and how many of them there are. I will develop the theoretical models necessary to answer this question. With this information, I will search for evidence of miniclusters in two ways. Firstly, they can be found with gravitational lensing in the same way planets around distant stars are found. Secondly, they show up as bursts of radiation when the miniclusters collide with magnetic fields e.g. of neutron stars. Understanding the minicluster masses and abundances is also very important to precisely predict the signal of axions in labs on Earth.